2009-12-10

70 MHz 25 W Power Amplifier

25W 4m PA by HA1YA

70 MHz PA

Circuit

This circuit we build on base of Mitshubishi Inc. application.The PCB and this construction is 100% our own design

The circuit is quite straight forward and consists of the following subparts:

An optional 50 Ω input attenuator.
The power module itself.
DC supply and bias circuit with appropriate RF decoupling.
An lowpass filter on the output.
An RF detector providing DC representation of the output power.

Fig 4. Output spectrum of the power module PA at V_DD = 13,8 V, I_DDQ = 1,5 A and 25 W.

Parts list

Resistors

Resistor	Value
R1, R2, R3	Optional Pi attenuator (see table below)
R4	390 Ω
R5	10 kΩ
VR1	100 Ω, trim pot
VR2	10 kΩ, trim pot

All resistors are 0,25 W/0,4 W and metalfilm type.

You have to select the value of R1, R2 and R3 according to your application. Under no circumstances may the input power level to the module exceed 100 mW. If used together with the 70 MHz transverter a 10 dB attenuation is required.

Attenuation	R1, R3 [Ω]	R2 [Ω]
0	Do not mount	Short
1	820	5,6
2	470	12
3	270	18
4	220	22
5	180	33
6	150	39
7	120	47
8	120	56
9	100	56
10	100	68

Capacitors

Capacitor	Value
C1, C2, C7, C8	1 nF
C3, C4, C6, C9, C10, C18	15nF
C5	100 µF, 25 V, electrolytic
C11	1 mF, 25 V, electrolytic
C12	4,7 pF
C13	15 pF
C14	27 pF
C15	56 pF
C16	18 pF
C17	1 pF

All capacitors are ceramic types unless otherwise stated.

Semiconductors

Component	Description
D1, D2	1N4148 or equivalent
D3, D4	1N5711 schottky diodes
IC1	78L05
IC2	RA30H0608M
Q1	BC177

Inductors

Inductor	Description
L1, L2	Ferrite beads
L3	122 nH, 5 turns, 6 mm inner diameter, 1 mm enamelled wire, 12 mm long
L4	85 nH, 5 turns, 6 mm inner diameter, 1 mm enamelled wire, 13 mm long

by Bo, OZ2M, www.rudius.net/oz2m